1. Field of the Invention
The present invention relates to motor-driven model airplanes and, in particular, to battery-powered motor-driven model airplanes of the pusher propeller type having a propeller disposed at the rear of the fuselage.
2. Description of the Prior Art
In the general design of actual airplanes, pusher-type airplanes with propellers behind the tail planes have often been considered because of excellent visibility provided for the pilot, higher safety in landing, taxiing and guidance, and also because of other advantages of these airplanes. In the case of model airplanes, pusher types driven by pusher propellers from behind are also desired because such models are less subject to damage when they collide unexpectedly in flight and also because they are less likely to cause bodily injuries, to operators than those models having a high speed propeller mounted on the nose. Also, the airframes of model airplanes having pusher propellers are free from aerodynamic influences of propeller slip streams, and practical designs for mounting pusher propellers on model airplanes have so far been awaited.
However, designing an engine-driven model airplane using a gasoline engine, which is a well known power source for radio controlled model airplanes, has been regarded as practically impossible.
For a model airplane well stabilized longitudinally and laterally, it is generally desirable to increase the distance between the position of the center of gravity of the entire airframe and the position of the tail plane, or the tail moment arm. In the case of a conventional model airplane driven by a gas engine, if it is a pusher-type model airplane, it is impracticable to mount the engine at the nose of the airframe because this engine would be heavy and the center of gravity would necessarily be shifted backward. In contrast to the above situation, the battery, which is the heaviest component of a model airplane of the present invention, can be mounted at the airframe nose of a pusher-type model airplane to obtain a satisfactorily large tail moment arm and hence high stability. In order to properly locate the center of gravity of the model airplane, it is necessary to mount the heavy engine close to main wings. Suppose that a model airplane, having an engine mounted inside the fuselage to meet the above requirement and a propeller behind the tail plane, is driven by an extension shaft of the engine. A strong mechanical structure will necessarily be required for mounting the propeller this way, in order to withstand the strong torsional force exerted on the propeller shaft and the extension shaft when the engine is started by compression. This means increased weight in the neighborhood of the tail plane and a shorter distance between the main wings and the tail plane and hence reduced longitudinal stability of the airplane.
Also, if the method of starting the engine with a string wound on a pulley attached to the engine output shaft is adopted, the engine cannot be enclosed within the fuselage; an opening with a lid has to be provided to the fuselage so that the opening is closed after the engine has been started, or else the engine is required to be mounted outside the fuselage.
However, an exposed engine mounted outside the fuselage has the particular drawback of being subjected to undesirable air resistance. Also, provision of a starter motor for the engine will mean additional weight of the entire airplane. Also, starting the engine requires not merely revolving the output shaft, but the choke and the needle valve must be adjusted. Because of these problems it has been considered impractical to enclose the engine within the fuselage. An additional requirement is that the radio equipment be spaced from the engine compartment to be free from engine dirt, which naturally constitutes a good deal of difficulty in designing the location of the center of gravity and the main wings. It has been considered practically impossible to build model airplanes with engines mounted inside the fuselages and having pusher propellers.
The present invention will solve these problems by means of a battery-powered, motor-driven model airplane.
In this connection, recently developed nickel-cadmium batteries, provided with gas release valves that act when the batteries are overcharged, are capable of quick charging. Because of their extremely small internal resistance, large discharge current of several amperes or more, relatively small size and light weight for their high current discharge, and quick charging time of a few minutes, these batteries have come into practical service for battery-powered motor-driven model planes.